The present invention relates to a camshaft driving arrangement for a double overhead camshaft (DOHC) engine having two camshafts for intake and exhaust valves at each of cylinder heads.
Japanese Patent Publication No. 60-50208 discloses a camshaft driving arrangement of the prior art as shown in FIG. 6.
Referring to FIG. 6, there is shown a DOHC engine. A crankshaft 2 is rotatably mounted to the cylinder block 1 at the lower portion thereof. A crankshaft sprocket 3 is mounted to the crankshaft 2.
Rotatably mounted to the cylinder head 4 are an intake camshaft 5 for intake valves (not shown) and an exhaust camshaft 6 for exhaust valves (not shown). Camshaft sprockets 7A and 7B are fixedly mounted to the ends of the camshafts 5 and 6, respectively. An idler gear 8 is rotatably mounted to the cylinder head 4 at the lower portion thereof. The idler gear 8 is formed with a large diameter gear 8A and a small diameter gear 8B.
A timing chain 9 drivingly interconnects the large diameter gear 8A of the idler gear 8 and the crankshaft sprocket 3, whereas a camshaft driving chain 10 drivingly interconnects the small diameter gear 8B of the idler gear 8 and the camshaft sprockets 7A and 7B.
For adjusting the tension of the timing chain 9, a movable tensioner 13 is arranged to the cylinder block 1. The movable tensioner 13 includes an arm 11A which has one end swingably mounted to the cylinder block 1 and touches the timing chain 9, and a tensioner body 11C which is provided with a presser 11B for urging the other end of the arm 11A toward the timing chain 9. On the other hand, for adjusting the tension of the camshaft driving chain 10, a movable tensioner 12 is mounted to the cylinder head 4. Additionally, there are provided fixed tensioners 13 and 14 for the timing chain 9 and the camshaft driving chain 10, respectively.
With such conventional camshaft driving arrangement, since the movable tensioners 11 and 12 are concealed by covers (not shown) for the timing chain 9 and the camshaft driving chain 10, respectively, the movable tensioners 11 and 12 are difficult to adjust. Thus, problems are encountered such that, while predetermined values of tension are applied to the timing chains 9 and the camshaft driving chain 10 by the movable tensioners 11 and 12, respectively, it is difficult to mount and remove the camshafts 5 and 6, the chains 9 and 10, and the idler gear 8. This decreases their assembly efficiency.
An object of the present invention is to provide a camshaft driving arrangement wherein camshafts and an idler gear are easy to install and remove.